1. Field of the Invention
The invention relates to a device for measuring pressures in a mold cavity of a casting mold that can be filled with melt, particularly a vacuum die-casting mold.
2. Description of the Related Art
DE 10140657 C1 already discloses a device for measuring pressures or a pressure progression in a mold cavity of a casting mold that can be filled with melt, particularly a vacuum die-casting mold, in which measurement channels are disposed in a direct connection with the mold cavity. These channels serve for direct pressure measurement in the mold cavity using a pressure sensor, and can be closed off during the melting, metering and/or mold-filling phase, using pins.
In DE 10140657 C1, it is accurately described that the demands on the quality of parts produced by means of die-casting methods, injection-molding methods or similar methods are constantly increasing. A quality improvement is also achieved by means of the further development of the production methods, wherein comprehensive knowledge of the individual process parameters is of great significance. During a casting process with preceding ventilation or evacuation of the casting mold, knowledge of the pressures that occur in the mold cavity, particularly during the mold-filling process, is an important parameter.
As an example, the importance of mold evacuation is explained in DE 10140657 C1, using the die-casting method. For example, in conventional die-casting, impurities in the cast structure of the parts, related to the method, are known. These impurities, in the form of pores in the die-cast part, occur as the result of enclosed air as well as parting agent and lubricant vapors. A significant reduction in the gas content in the case part is achieved by means of the use of vacuum. In this connection, a partial vacuum acts on the entire mold cavity, including the casting chamber and the material intake pipe, so that air, vapors and gases that occur are drawn off. Metering, filling of the casting chamber, of the casting flow system, and at least of parts of the mold cavity take place.
It is absolutely necessary, however, to detect the pressure conditions directly in the mold cavity in order to establish the amount and the time of the partial vacuum, and to achieve quality assurance.
In DE 39 39 728 A1, a pressure measurement device for die-casting and injection-molding machines is disclosed. Advantageous measurement directly in the mold cavity is pointed out, but because of the expected damage to the sensors, this path is viewed as not being implementable for rough casting operation. For this reason, DE 39 39 728 A1 proposes that the pressure measurement device measures pressures exclusively by way of the casting mold and not directly in the mold cavity. In this connection, the sensor is not exposed to the destructive effect of the melt.
From EP 0 600.324 A1, it is known to measure the pressure in the region of the vacuum valve. In this connection, the pressure sensor is protected ahead of the metal front by closing the valve.
From DE 195 00 005 C2, a method and an apparatus for pressure measurement in a die-casting mold or injection-molding mold are known, in which the pressure measurement takes place by way of gaps. In this connection, the gaps are disposed in a metallic permanent mold, perpendicular to the unmolding direction. On the one side, the gaps are connected with the mold cavity directly or by way of an inflow system, and on the other side, they are connected with a pressure sensor, directly or by way of an inflow system. The gaps have almost parallel surfaces. The surfaces that form an individual gap are disposed in part in what is called the furnace side and in part in what is called the ejector side of the permanent mold. It is supposed to be possible to measure pressures that correspond to the pressures in the mold cavity, in almost error-free manner, by way of the gaps that connect the mold cavity with the pressure sensor. In this connection, the measurement channels are closed off by the solidifying metal melt, and the pressure sensor is protected accordingly. In particular, it is supposed to be possible to use the method in aluminum die-casting and zinc die-casting.
In the aforementioned state of the art, closing of measurement channels by means of pins, valves, and solidifying melt is therefore known.